Current Status of Cardiac CT for Nuclear Medicine Professionals: Coronary Artery Disease Evaluation

Abstract

With advances in computed tomography (CT) technology over the past two decades, cardiac CT has become a noninvasive diagnostic tool for morphological evaluation of coronary artery disease (CAD) caused by atherosclerotic plaques and stenosis and serves as a “gatekeeper” before invasive coronary angiography. Additionally, cardiac CT stress perfusion and CT-derived fractional flow reserve can be used to assess the hemodynamic significance of coronary artery stenosis. Delayed enhancement CT can detect and localize myocardial infarction and assess myocardial viability. Currently, cardiac CT serves as a potential “one-stop-shop” imaging modality for the comprehensive assessment of patients with suspected or known CAD by providing analysis of coronary anatomy, functional significance, and characterization of left ventricular myocardium in a single session. It is crucial for nuclear medicine professionals to be aware of the current capability of cardiac CT and its ability to perform comprehensive and accurate nuclear cardiac imaging studies, which are essential for functional assessment of CAD.

Introduction

Despite breakthroughs in cardiovascular medicine, coronary artery disease (CAD) is increasingly prevalent in modern society and is one of the leading causes of death worldwide [1]. With advances in computed tomography (CT) technology over the past two decades, cardiac CT angiography (CCTA) has become the cornerstone of noninvasive evaluation of CAD by providing direct and detailed morphological assessment of coronary artery stenosis and atherosclerotic plaques [2]. CCTA can accurately diagnose coronary artery stenosis ≥ 50% but cannot diagnose hemodynamically significant stenosis causing myocardial ischemia [3]. Modern technology in CT scanners and improvements in cardiac-specific analysis software have enabled quantification of atherosclerotic plaques and functional imaging, including CT-myocardial perfusion imaging (CT-MPI) and CT-derived fractional flow reserve (CT-FFR). For patients with stable chest pain with or without CAD, the combination of CCTA with CT-FFR or CT-MPI may help identify patients who require invasive coronary angiography (ICA) or guideline-directed medical treatment [4]. Myocardial delayed enhancement CT (MDE-CT) enables accurate determination of the location and extent of acute and chronic myocardial infarction (MI), similar to late gadolinium enhancement magnetic resonance imaging (LGE-MRI) [5]. Nuclear medicine professionals can benefit from incorporating cardiac CT into their practice because of the anatomical and functional information it provides to increase the accuracy of CAD diagnosis and evaluation.

CCTA for Coronary Calcium Score, Coronary Atherosclerotic Plaque and Stenosis

Coronary calcium scan with electrocardiogram (ECG)-gated noncontrast cardiac CT allows direct visualization and quantification of calcified atherosclerotic plaques. Coronary artery calcification (CAC) is defined as a hyperattenuating lesion with an area of ​​at least 3 contiguous pixels (at least 1 mm²) and exceeding a threshold of 130 Hounsfield units. CAC is traditionally quantified by the Agatston score [6] (Fig. 1). Coronary calcium score is closely associated with the overall burden of coronary artery plaque and has been strongly associated with the occurrence of major cardiovascular events, including non-fatal myocardial infarction, cardiac death, and all-cause mortality, in mid- to long-term follow-up studies [7, 8]. Current guidelines have recommended the use of CAC scoring for cardiovascular risk assessment, particularly in the intermediate-risk population (defined as individuals with a Framingham risk score-estimated 10-year risk of developing cardiovascular disease between 10% and 20%) [9]. While the absence of CAC does not completely exclude the presence of atherosclerosis in the coronary arteries, it is associated with a lower likelihood of significant coronary artery stenosis and a lower risk of experiencing a myocardial infarction or cardiac death in the near future, typically within the next 2 to 5 years [10]. Follow-up CAC testing plays a valuable role in the ongoing management of cardiovascular disease by providing reassessment of atherosclerotic cardiovascular disease risk in calcium-negative patients, evaluating treatment effectiveness, and guiding therapeutic decisions to optimize cardiovascular risk reduction strategies [9].

Fig. 1.

A 63-year-old man who underwent a coronary artery calcium scan for a health checkup

Coronary artery calcium in the left anterior descending coronary artery (arrows). The Agatston score was 215.8, indicating a moderate coronary artery calcium score

In CCTA, the severity of coronary artery stenosis is determined based on the degree of maximum internal diameter stenosis. If the internal diameter stenosis is ≥ 50%, it is diagnosed as morphologically significant stenosis. CCTA has a much higher sensitivity for diagnosing coronary artery stenosis than CCA and has a negative predictive value of 95–99% [11, 12]. It allows for assessing the status of coronary artery in patients with suspected or known CAD including the presence and severity of stenosis and the characteristics of atherosclerotic plaques. CCTA is favored in patients < 65 years of age with intermediate to high pretest likelihood of CAD [4].

CCTA is currently considered a noninvasive imaging tool for evaluating and managing CAD in clinical practice and acts as a “gatekeeper” before ICA (Fig. 2). However, CCTA is known to overestimate or underestimate coronary artery stenosis compared to ICA because of technical limitations [13] (Fig. 3). According to the American College of Cardiology/American Heart Association (ACC/AHA) guidelines, among patients at intermediate-high risk with stable chest pain and no known CAD, CCTA is useful for the diagnosis of CAD and for risk stratification [14]. In 2013, the European Society of Cardiology (ESC) proposed that CCTA be used as an alternative to cardiac stress imaging tests as a priority evaluation for patients with chest pain and stable CAD [15]. Recently, the UK National Institute for Health and Care Excellence (NICE) guidelines recommended CCTA as the highest-priority evaluation method for CAD regardless of the pre-test probability of CAD [16].

Fig. 2.

A 65-year-old man smoker with hypertension complained of chest pain for 3 weeks

Curved multiplanar reformatted (MPR) CT images of the left anterior descending coronary artery (A) and left circumflex artery (B) demonstrate significant stenoses with noncalcified atherosclerotic plaque with positive remodeling in the left main coronary artery (LM, arrow) and proximal left anterior descending coronary artery (LAD, arrowhead). The right coronary artery (RCA, C) is normal. Invasive coronary angiography images show severe stenosis in LM-proximal LAD (arrows, D) and normal RCA (E)

Fig. 3.

A 71-year-old man smoker with hypertension and dyslipidemia complained of chest pain for 1 month

Curved multiplanar reformatted (MPR) CT images of the left anterior descending coronary artery (LAD) demonstrates insignificant stenosis with mixed noncalcified and calcified atherosclerotic plaques with positive remodeling in the mid-LAD (arrow). Invasive coronary angiography image shows insignificant stenosis in the mid-LAD with fractional flow reserve of 0.78 (arrows, B). Dynamic stress perfusion CT image (C) demonstrates no significantly reduced myocardial blood flow in the left ventricular wall

Invasive FFR was ≤ 0.80 in 83 (35%) vessels with obstructive lesions and in 17 (7%) vessels without obstructive lesions [17]. In the Fractional Flow Reserve Versus Angiography for Multivessel Evaluation (FAME) study [18], only 35% of vessels with 50–70% internal stenosis showed hemodynamically significant stenosis in invasive FFR, indicating a discrepancy between the morphological severity of the lesion and its hemodynamic significance. In other words, because morphological stenosis of the coronary artery does not correspond to hemodynamically significant stenosis causing myocardial ischemia, defined as invasive FFR < 0.80, the presence of morphological stenosis alone is misinterpreted and affects clinical decision-making.

The analysis of plaque morphology by CCTA is becoming increasingly important. High risk plaque or vulnerable plaques includes low-attenuation < 30 Hounsfield units (HU), positive remodeling ≥ 1.1, spotty calcifications < 3 mm, and napkin ring sign. (Fig. 4). Quantitative parameters obtained from CCTA increase the diagnostic accuracy of functionally significant coronary artery stenosis compared to that of internal diameter stenosis. Park et al. [19] demonstrated that percent aggregate plaque volume (the sum of plaque volume divided by the sum of vessel volume from the ostium to the distal portion of the lesion) and atherosclerotic plaque characteristics (positive remodeling, low attenuation plaque, and spotty calcification) enabled better identification of hemodynamically significant coronary lesions as measured by using invasive FFR. According to a study by Nakazato et al. [20], in patients with moderate stenosis (30–69% internal diameter stenosis), the areas under the curve (AUC) for invasive FFR were percent aggregate plaque volume (0.85), minimum internal diameter area (0.78), minimum internal diameter (0.75), diameter stenosis (0.68), and area stenosis (0.66) in that order. Compared to diameter and area stenoses, percent aggregate plaque volume improved the identification, discrimination, and reclassification of myocardial ischemia in moderate stenosis. Driessen et al. [21] reported the association between quantitative plaque burden and plaque morphology obtained using CCTA and positron emission tomography (PET)-derived myocardial blood flow (MBF) and invasive FFR. Plaque length and volume, minimal lumen area, and > 70% lumen stenosis were significantly associated with impaired hyperemic MBF and invasive FFR. Partially calcified plaques, positive remodeling, and low attenuation plaque displayed a negative impact on hyperemic MBF and invasive FFR. In particular, positive remodeling and noncalcified coronary atherosclerotic plaque volume reduced both MBF and invasive FFR independent of luminal stenosis. Including the characteristics of adverse atherosclerotic plaque to the assessment of coronary stenosis severity allows for better identification of myocardial ischemia compared to luminal stenosis assessment alone. Evaluation of atherosclerotic plaque morphology using CCTA has become an essential component of the diagnostic evaluation and risk stratification of patients with CAD. Incorporating information about plaque characteristics into treatment decisions can help optimize patient care and improve clinical outcomes [22].

Fig. 4.

Atherosclerotic plaque analysis by cardiac CT angiography (CCTA)

Based on CCTA, the plaque type is classified as (A) calcified plaque (arrow), (B) noncalcified plaque (arrow), or (C) partially calcified or mixed calcified and noncalcified plaque (arrow). High risk or vulnerable plaque features are classified as (D) positive remodeling + spotty calcified plaque (arrow), (E) positive remodeling + low-attenuation plaque (arrow), and (F) napkin ring sign (noncalcified plaque with enhancing ring, arrow)

Myocardial Ischemia Using Stress Perfusion CT

If there is coronary artery stenosis, resting blood flow remains normal for a considerable period of time due to compensatory vascular dilatation. Therefore, even when coronary artery stenosis progresses to 80%, perfusion abnormalities may not be observed on resting myocardial perfusion imaging. However, coronary arteries with stenosis > 50% show a coronary steal phenomenon in which compensatory dilatation can no longer occur, resulting in ischemia in the myocardium [23]. Compared to vasodilator stress nuclear medicine myocardial perfusion imaging, stress perfusion cardiac magnetic resonance (SP-CMR) has superior spatial resolution and does not involve radiation exposure; therefore, it is currently the recommended imaging method [24]. However, SP-CMR is not prevalently used because of several limitations such as limited availability, long scan time, high cost, and contraindications.

CT-MPI is performed in the same manner as SP-CMR [25, 26]. The sequence for stress and rest perfusion imaging involves performing the stress phase first to avoid delayed contrast effects. In principle, the interval between the two examinations is at least 10 min after the first injection of contrast agent. Contrast agent is injected at a rate of 4 ∼ 5 ml/sec using a high-speed contrast agent automatic injector. Ischemic areas appear to have reduced blood flow or hypoenhancement in the left ventricle (LV) myocardium during the stress phase but normal blood flow or normal enhancement in LV myocardium during the rest phase, resulting in a reversible perfusion defect. Myocardial infarction/fibrosis manifests as persistent hypoenhancement or reduced blood flow (persistent perfusion defect) due to decreased blood flow during stress and rest phases. CT-MPI has several potential advantages over SP-CMR including wider availability, shorter scan time, reduced motion artifacts, full cardiac coverage with high 3D isotropic resolution, and lower cost. Limitations include exposure to ionizing radiation and the use of iodinated contrast agent, which may not be appropriate for all patients. Low contrast-to-noise ratio and the presence of beam hardening artifacts are the drawbacks of CT-MPI [27].

CT-MPI is divided into two methods (dynamic and static CT-MPIs) depending on the time and number of images of CT scans obtained by injecting contrast agent (Fig. 5). Table 1 shows a direct comparison of the static CTP and dynamic CTP. Dynamic CT-MPI acquires dynamic images by obtaining multiple CT data along the myocardial time-attenuation curve, and the absolute value of MBF can be found by calculating the upslope of myocardial contrast enhancement [26] (Fig. 6). The cutoff values of MBF to identify hemodynamically significant coronary artery stenosis vary considerably between studies, ranging from 75 to 164 mL/100 mL·min. Normalizing regional MBF values relative to the measure of global MBF appears to enhance the diagnostic accuracy of dynamic CT-MPI [28]. Dual-source CT scanner with shuttle mode and wide-area detector CT scanner with whole heart volume scan are used for dynamic CT-MPI. In a meta-analysis of dynamic CT-MPI [29], compared to other ischemia imaging techniques, the pooled sensitivity and specificity of MBF were 0.83 (95% confidence interval (CI): 0.80–0.86) and 0.90 (95% CI: 0.88–0.91), respectively, at the segment level, 0.85 (95% CI: 0.80–0.88) and 0.81 (95% CI: 0.78–0.84), respectively, at the vascular level and 0.93 (95% CI: 0.82–0.98) and 0.82 (95% CI: 0.70–0.91), respectively, at the patient level, showing very high diagnostic accuracy in identifying myocardial ischemia. These results are superior to those of static CT-MPI. The presence and number of perfusion defects were associated with a higher risk of major adverse cardiac events (MACEs) and this increased beyond coronary artery stenosis and clinical risk factors on CCTA [30]. Dynamic CT-MPI can be a useful tool in the evaluation of patients with severe coronary calcification, coronary stents, or inconclusive results from other tests in the context of suspected CAD [27].

Fig. 5.

Static versus dynamic CT myocardial perfusion imaging. The image represents the tissue attenuation curves for the left ventricle and myocardial territories. In static CT imaging (light green), a single scan is obtained typically at the peak of contrast enhancement within the myocardium. In dynamic CT imaging (light purple), multiple scans are acquired at different time points during the passage of contrast through the myocardial tissue

Table 1.

Comparison between static CT perfusion versus dynamic CT perfusion

	Static CT perfusion	Dynamic CT perfusion
CT scanner	Recommended for all CT scanners, typically 64-detector and higher CT scanners	2nd & 3rd generation dual-source CT scanners 320-wide area detector CT scanner
Imaging interpretation	Qualitative (mainly)/semi-quantitative	Quantification of myocardial blood flow and volume
Coronary artery evaluation	Possible	Impossible
Beam-hardening artifact	Yes	Yes
Breath holding	Shorter	Longer
Radiation dose	Lower	Higher
Other inherent limitations to consider	Risk of underestimation or overestimation of perfusion Limited assessment of microvascular disease and multi-vessel disease	Complex image acquisition and processing Necessary for standardized protocol for image acquisition, analysis and interpretation

Fig. 6.

A 62-year-old man with hypertension and dyslipidemia complained of effort-induced chest pain

Curved multiplanar reformatted (MPR) CT image of the left anterior descending coronary artery (LAD, A) shows calcified plaques in the left main, mid-left anterior descending coronary, and proximal left circumflex coronary arteries. Significant stenosis with noncalcified plaque is seen in the mid LAD and ostium of the first diagonal branch (D1, arrow)

Adenosine dynamic stress perfusion CT images (B, C) demonstrate perfusion defects (B) and markedly reduced myocardial blood flow (C) in the anterior and anteroseptal left ventricular wall

CT-derived fractional flow reserve (FFR) image (D) shows low FFR values in the mid LAD (arrow) and D1 (arrowhead) distal to significant stenosis of the mid LAD. Invasive coronary angiography (E) reveals discrete concentric 90% diameter stenosis at the mid LAD-D1 bifurcation (arrow)

Single-energy static CT-MPI obtains a single CT data at the predicted time of maximum myocardial enhancement, usually 7–16 s after HU 100–150 in the enhanced aorta, and visually analyzes the difference in myocardial attenuation to diagnose myocardial ischemia [26, 31] (Fig. 5). Single-energy static CT-MPI visually detects myocardial ischemia under maximum contrast enhancement. However, dynamic CT-MPI measures the absolute value of contrast-enhanced MBF and is more likely to accurately detect myocardial ischemia in cases of moderate stenosis or multiple vessel involvement. Dual-energy static CT-MPI employs dual energy CT technology, which utilizes X-rays of two different energy levels (for example, 80 kV and 140 kV or 100 kV and 140 kV) to provide enhanced diagnostic information [32]. In addition to visual assessment of myocardial perfusion, iodine distribution maps provide quantification of myocardial iodine uptake (mg iodine per milliliter) to distinguish between normal myocardium and ischemic or necrotic myocardium. A meta-analysis of static CT-MPI [33]. showed that it had good agreement with single photon emission computed tomography and SP-CMR. On a per-patient level, sensitivity, specificity, and AUC were 0.85 (95% CI: 0.70–0.93), 0.81 (95% CI: 0.59–0.93), and 0.90 (95% CI: 0.87–0.92), respectively. On a per-vascular level, sensitivity, specificity, and AUC were 0.80 (95% CI: 0.67–0.88), 0.81 (95% CI: 0.72–0.88), and 0.87 (95% CI: 0.84–0.90), respectively. When comparing the combination of CCTA and static CT-MPI to CCTA alone, specificity increased from 0.62 (95% CI: 0.52–0.70) to 0.84 (95% CI: 0.74–0.91) at the patient level (p = 0.008) and from 0.72 (95% CI: 0.63–0.79) to 0.90 (95% CI: 0.85–0.93) at the vascular level (p = 0.001) without a significant decrease in sensitivity.

The combination of CCTA and CT-MPI provides a comprehensive noninvasive evaluation of moderate to severe (≥ 50% stenosis) coronary artery lesions [2]. If the CCTA is positive but the CT-MPI is negative, there is no significant hemodynamic coronary stenosis. If the CCTA is negative but the CT-MPI is positive, the possibility of artifacts or myocardial ischemia and absence of obstructive coronary arteries should be considered. If both tests are negative, further evaluation of CAD using ICA is not necessary unless there is a strong clinical suspicion of stenotic CAD. If both tests are positive, it points to the presence of significant CAD, and ICA should be considered as the next step after risk stratification and consideration of the patient’s clinical status [34, 35]. Compared to CT-FFR, CT-MPI has several advantages, particularly in patients with extensive coronary calcification, chronic coronary occlusions, previous percutaneous coronary intervention (PCI), and microvascular angina [27]. Although CT-MPI is included in CAD-RAD 2.0, evidence of the potential role of CT-MPI with CCTA in the identification of significant CAD and its role in guidance for ICA is lacking. CT-MPI requires rigorous clinical validation and ongoing research to establish its role in identifying significant CAD in clinical practice [2, 4].

Myocardial Ischemia Using CT-derived FFR

The invasive FFR using a guide wire with a pressure sensor is generally measured in the state of maximum hyperemia induced by adenosine and is defined as the ratio of the pressure in the aorta to the pressure at a distant point near the stenosis. It is used to localize myocardial ischemic lesions in angiography, and FFR ≤ 0.8 is defined as the cutoff value to determine whether PCI procedures should be performed; it results in improved clinical outcomes when compared to PCI performed using angiography alone [36]. FFR is now recognized as the standard for myocardial ischemia testing in CAD [37], although it is an invasive procedure, and there are risks such as drug-induced hyperemia, need for additional procedure time, and the resulting patient discomfort and complications.

Recently, computational fluid dynamics has been applied to obtain the three-dimensional geometric structure of the coronary artery from conventional CCTA images and calculate the peripheral resistance of the heart using myocardial mass obtained from CT and simple physiological data (blood pressure and heart rate) using computer simulation technology. Many studies have shown the strong correlation and diagnostic performance of CT-FFR in assessing the functional significance of coronary artery stenosis, using invasive FFR as the reference standard [37–40]. In a recent study by Norgaard et al. [41] that evaluated patients with moderate coronary stenosis (30–70% stenosis), CT-FFR ≤ 0.8 accurately identified 73% of the patients and 70% of the vessels compared to invasive FFR. Additionally, patients with CT-FFR > 0.8 did not undergo further angiography and had no MACEs during the 12-month follow-up. In a meta-analysis by Zhuang et al. [42], the pooled sensitivity and specificity of CT-FFR for the detection of myocardial ischemia were 89% (95% CI: 85–92%) and 71% (95% CI: 61–80%), respectively, at the patient level and 85% (95% CI: 82–88%) and 82% (95% CI: 75–87%), respectively, at the vascular level, compared to invasive FFR as reference. In particular, the specificity of CT-FFR was higher than that of CCTA at both patient (0.71 vs. 0.32) and vascular levels (0.82 vs. 0.46). CT-FFR offers incremental diagnostic value than CCTA alone for identifying hemodynamically significant coronary artery lesions, reduces the need for ICA by decreasing nonobstructive disease at ICA, and provides guidance for revascularization decisions and planning [43]. CT-FFR is currently used clinically in the United States and Europe but is not used in Korea because it is not covered by medical insurance. Compared to the requirement for off-site supercomputers to perform massive calculations in the field of computational fluid dynamics, an on-site computation of CT-FFR based on machine learning (ML) using an independent workstation has been developed and is being used for research purposes [44]. ML-based CT-FFR is a less computationally intensive and time-consuming approach compared to the conventional off-site CT-FFR method, while still offering comparable diagnostic performance for identifying the hemodynamic significance of coronary artery stenosis (Fig. 6). In a meta-study by Tan et al. [45], conventional off-site CT-FFR showed better diagnostic accuracy than ML-based CT-FFR at the vascular level (pooled sensitivity 0.73 [0.66, 0.80] vs. 0.72 [0.62, 0.83], p = 0.04 and pooled specificity 0.93 [0.88, 0.98] vs. 0.87 [0.78, 0.97], p = 0.010). Although it has not yet been used clinically, ML-based CT-FFR opens the possibility for CT-FFR to be widely used [46]. CT-FFR cannot be used to evaluate microvascular angina, coronary stents, coronary artery dissection, coronary emboli, congenital coronary artery anomalies, and coronary artery bypass graft [43]. CT-FFR is recommended to assess the hemodynamic significance of CAD and guide treatment decision according to recent guidelines. However, the integration of CT-FFR into clinical practice may be influenced by factors such as the commercial availability of CT-FFR, consensus among cardiac multidisciplinary team experts, and regulatory approval in various regions [2, 4].

Myocardial Delayed Enhancement CT (MDE-CT)

The principle of MDE-CT, similar to that of LGE-MRI, is that the cell membrane of necrotic myocytes ruptures, and the iodinated contrast agent accumulates in the intracellular space of the necrotic myocytes. In chronic MI, necrotic myocytes are replaced by scar tissue, resulting in expanded extracellular space and increased contrast agent accumulation. MDC-CT images are typically taken 10 min after administration of contrast agent with low-dose acquisition protocol utilizing a lower tube voltage and prospective electrocardiogram- triggered or high-pitch mode [5]. Dual-contrast phase CT imaging showed that compared to normal myocardium, the myocardium in the infarct area has hypoenhancement in the early phase image and subendocardial or transmural hyperenhancement or central hypoenhancement with peripheral hyperenhancement in the delayed phase [47, 48] (Fig. 7). Sato et al. [49] found three types of MDE patterns: transmural, subendocardial, and no DE on MDE-CT immediately after primary PCI in patients with acute MI. In patients with transmural DE, the recovery in global LV function was significantly worse while LV remodeling was significantly increased compared to patients with subendocardial DE and no DE. The combination of central hypoenhancement and peripheral or surrounding hyperenhancement in the MI area correlates better with LV wall thinning, ejection fraction, microvascular obstruction, and LV remodeling than hyperenhancement alone and is indicative of future MACE [50–55]. It is difficult to expect functional recovery even with reperfusion treatment in the central core of hypoenhancement in the myocardial area showing microvascular occlusion [53]. Dual-energy CT with MDE demonstrated accurate detection and localization of myocardial scar when compared to LGE-CMR as a reference [54]. Accordingly, MDE-CT imaging has the potential to evaluate the size of MI and myocardial viability and serve as an independent prognostic factor for MACEs [5]. However, due to the low contrast-to-noise ratio of CT between abnormal and normal myocardium, the diagnostic accuracy is relatively low compared to LGE-CMR images, which limits its widespread use as an imaging diagnostic method for evaluating myocardial viability. There are several techniques to maximize the contrast-to-noise ratio of MDE-CT images, including low-tube-voltage imaging, dual-energy-based iodine imaging, and iterative reconstruction. Nishii et al. [55] demonstrated that a deep learning denoising model supervised with average CT images significantly reduced image noise to 28% of the original level in the LV blood pool and improved specificity and accuracy (93.1% and 93.8%, respectively) compared to standard averaged images (87.9% [p = 0.007] and 88.5% [p = 0.009], respectively) for MDE patterns (transmural, epicardial, mid-layer, and subendocardial) (Fig. 8). Currently, MDE-CT is still considered investigational and has not been widely adopted in clinical practice for the assessment of myocardial scarring or fibrosis. Research and development of cardiac CT imaging technology is ongoing, and future advances may lead to the inclusion of MDE-CT into clinical guidelines [52].

Fig. 7.

A 58-year-old man with acute myocardial infarction

Short-axis myocardial delayed contrast-enhanced cardiac magnetic resonance imaging (MRI, A) shows transmural delayed enhancement (arrows) with subendocardial hypoenhancement (arrowhead), indicating microvascular occlusion in the mid-inferior septum and inferior and inferolateral left ventricular (LV) wall

Early contrast enhancement short-axis multiplanar reformatted (MPR) CT image (B) shows subtle hypoenhancement (arrows) in the subendocardium of the mid-inferior LV wall. Delayed contrast enhancement short-axis MPR CT image (C) shows transmural delayed enhancement (arrows) with subendocardial hypoenhancement LV wall (arrowhead) which is identical to the cardiac MRI finding

Volume rendered CT image (D) depicts stenoses of left anterior descending coronary artery (LAD, arrow) and first diagonal branch (D1, arrowhead) spatially and three-dimensionally, enabling easy recognition. Curved MPR images of right coronary artery (E), LAD (F), D1 (G), and large obtuse marginal branch (OM, H) show multiple significant stenoses (arrows)

Invasive coronary angiography reveals severe stenoses (> 80% lumen reduction) in the mid LAD (arrow), D1(arrowhead), and OM (long arrow) (I) and thrombotic occlusion in the posterolateral branch (J). Right coronary artery ectasia (arrowheads) is also present

Fig. 8.

Short-axis myocardial delayed contrast-enhanced image of a 31-year-old man with acute myocardial infarction

Cardiac magnetic resonance imaging (MRI, A) shows transmural delayed enhancement (arrows) with subendocardial hypoenhancement (arrowheads), indicating microvascular occlusion in the mid inferior septum and inferior and inferolateral left ventricular (LV) wall

Artificial intelligence-based contrast-enhanced and denoised CT (B) image had less noise and more contrast enhancement for subendocardial hypoenhancement (arrowheads) and transmural enhancement (arrows) of the LV wall mentioned above compared to standard CT image (C)

Conclusion

Over the past two decades, the application of cardiac CT has expanded beyond the morphological assessment of coronary artery stenosis to the characterization and quantification of atherosclerotic plaques, CT-FFR and CT-MPI for identification of the hemodynamic significance of coronary artery stenosis, and MDE-CT for the detection and localization of MI and myocardial viability assessment in patients with known or suspected CAD, allowing comprehensive assessment of CAD. Recently, artificial intelligence has been utilized to improve cardiac CT image quality, automated coronary stenosis assessment and atherosclerotic plaque quantification, and ML-based CT-FFR. Continual advancements in CT scanning technology, post-processing, and cardiac-dedicated software, and the integration of AI have further enhanced the role of cardiac CT in providing accurate and comprehensive information regarding CAD. Being aware of the current status of cardiac CT and its role in the assessment of CAD is crucial for nuclear medicine professionals to perform comprehensive and accurate nuclear cardiac imaging tests.

Author Contributions

Sung Min Ko participated in the drafting of the manuscript and approved the final content.

Funding

None.

Data Availability

Not applicable.

Declarations

Conflict of Interest

Sung Min Ko declares that he has no conflict of interest.

Ethics Approval

All content in this editorial complies with the ethical standards of the institutional and/or national research committee, as well as the 1964 Helsinki declaration and its later amendments or equivalent ethical standards.

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For this editorial article, obtaining informed consent was waived.

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Not applicable.